On January 15, 1975, Walt Disney World's Space Mountain rollercoaster opened to the public. It was the key feature of Tomorrowland at the Magic Kingdom.
An enormous pageant was held to celebrate the event, featuring "thousands of flying doves, a pageant of nations, a 2000-member band, 50,000 balloons," and red, white, and blue fireworks. Mercury 7 pilot Scott Carpenter and a handful of other astronauts were on hand.
Here's the most exciting bit of the opening ceremony:
And if that's not enough celebration for you, let's put it in the larger 48-minute context of this groovy TV special: